1. Field of the Invention
This invention relates to a speed-increasing and accumulating conveyor chain that can transfer (i.e., increase the speed of) an object to be transferred at a transfer speed faster than the traveling speed of the chain and that can stop (i.e., accumulate) the object while causing the chain itself to continuously travel.
2. Prior Art
Japanese Patent Publication No. HEI. 5-11212 discloses a speed-increasing and accumulating conveyor chain as a conventional example. In a chain of this type, a large-diameter mounting roller and small-diameter traveling rollers are rotatably fitted loosely around a plate connecting pin concentrically through a bushing. The chain has both the function of increasing the speed of an object to be transferred and the function of accumulating such object. That is, when transferring the object while increasing its speed, a frictional force over the rotating surface between the mounting roller and the traveling rollers allows the traveling rollers that are rolling over the rails to gradually impart a rotating force to the mounting roller, thereby causing both the traveling rollers and the mounting roller to roll integrally with one another. The ratio between the diameter of the traveling roller and that of the mounting roller makes the transfer speed of the object faster than the traveling speed of the chain, thereby transferring the object at the increased speed. On the other hand, at the time of accumulation in which the object to be transferred is stopped while abutted against a stopper (i.e., an object stopping unit), slippage is caused between the traveling rollers that are rolling over the rails and the mounting roller that tends to stop. This causes the mounting roller to reversely rotate with respect to the traveling rollers, thereby allowing the object to be stopped at a predetermined position.
The chain of this type has many traveling rollers and mounting rollers arranged along the chain. When the friction coefficient between these rollers and the bushings and the friction coefficient between the bushings and the connecting pins are large, the traction force of the chain as a whole increases, which in turn requires a large chain-driving force. If the traveling rollers and the mounting rollers are made of resin, the friction coefficient between the traveling rollers and the mounting rollers is relatively stable. However, if the traveling rollers and the mounting rollers are made of steel in particular, a lubricating oil or the like is applied between these steel rollers and the bushings and between the bushings and the connecting pins in order to reduce the chain-driving force by stably maintaining the friction coefficient between the traveling rollers and the mounting rollers at a low level.
However, when the oil runs out in such a chain, the friction coefficient between the traveling rollers and the mounting rollers increases, thereby increasing the traction force of the chain as a whole. Thus, from this arises a problem that a large chain-driving force is required. Further, when the oil runs out among these steel rollers, the bushings and the connecting pins, noises such as sliding noises among them and bending noises produced when the chain meshes with sprockets are e caused. These noises impose the restriction of not allowing the chain to be used in quiet working environments in various types of manufacturing industries. Additionally, dust is produced by abrasion, thereby imposing the restriction of not allowing the chain to be used in clean working environments in such manufacturing industries as food, medical and electronic industries.
Still further, when the friction coefficient between the mounting rollers and the object to be transferred increases under an unstable condition at the time of accumulation, so does a force for stopping the object while operating the chain (i.e., line pressure), thereby often causing the trouble of breaking the stopper. Moreover, when the friction coefficient between the mounting rollers and the object to be transferred fluctuates when the accumulating function is reset to increase the speed, the chain is not stably activated to the desired transfer speed. This makes smooth transfer difficult, thus causing negative effects on the process control of a production line.
When oil is lubricated in order to reduce abrasion-caused elongation, sliding noises and bending noises caused between the connecting pins and the bushings of such a speed-increasing and accumulating conveyor chain, the lubricating oil enters into or deposits on portions where the traveling rollers are in contact with the mounting rollers and the outer circumferential surfaces of the traveling rollers. The lubricating oil does retard the acceleration of the transfer speed or does not allow the traveling rollers and the mounting rollers to rotate. Thus, from this arises a problem that the speed-increasing function is not performed sufficiently.